The invention is intended for the analysis of the wave surface of a light beam.
This type of analysis enables optical elements to be checked, and optical apparatus to be certified. It also permits the study of physical phenomena not measurable directly, such as variations in optical index within turbulent environments that may be encountered when passing through the earth's atmosphere, or in a wind-tunnel air stream, for example.
The so-called "Hartmann-Shack" analyser is known, described in "Phase measurements systems for adaptative optics", J. C. WYANT, AGARD Conf. Proc., No 300, 1981. The general working principle consists of optically conjugating the phase defect to be analysed with a grid of micro-lenses. In the common plane of the foci of the micro-lenses, an interferogram is observed, consisting of a lattice of spots, deformed according to the gradients of the wave surface.
This type of wave surface analyser has the advantage of functioning in polychromatic light, so long as the operating difference defect to be detected is not dependent on the wavelength. The light output is very good; on the other hand, the sensitivity and the dynamics can be adjusted only by changing the grid of micro-lenses.
In its European patent application EP-A-0538126, the applicant described a trilateral shift interferometer. Through a mirror-based assembly, the beam to be analysed is optically subdivided, in a conjugate plane of the defect, into three sub-beams. A special optical treatment of the three sub-beams thus obtained enables an interferogram to be observed which is sensitive to the gradients of the wave surface, and this with a possibility of continuous adjustment of the dynamics and of the sensitivity. It is also possible to estimate the error in measuring from the measurement itself; finally, the system of interference fringes obtained is easy to interpret, and particularly suited to analysis techniques based on Fourier transforms. On the other hand, this apparatus functions only with monochromatic light, and its light output is not as high as that of the Hartmann-Shack analyser.
It therefore appears to be extremely desirable to have an interferometer possessing both the flexibility of adjustment of the interferometer with trilateral shift of EP-A-0538126, and the light output of the Hartmann-Shack analyser.